The invention relates to the measurement of adipose tissue and lean tissue using ultrasonic methods, compositions and devices, particularly methods, compositions and devices that facilitate placement of ultrasonic probe(s) using external anatomic landmarks, such as the umbilicus, and improve the reproducibility of ultrasonic measurements of object layer thickness.
Objects often include layers of different compositions that are difficult to measure directly and accurately. In many cases, the object""s interior can not be accessed to allow for direct measurement. It may be impractical to intrude the object""s interior or, if even using non-invasive techniques, it may be difficult to position the probe for accurate measurements.
For measurements of biological specimens, the thickness of underlying layers are particularly inconvenient to measure. Many such measurements are preferably taken in vivo, which makes invasive techniques impractical. If non-invasive techniques are used, they are often susceptible to operator errors and can be quite costly, as in the case of expensive medical diagnostic equipment.
In the case of body adipose tissue layers, measurements with skin calipers and water immersion tanks can be used to assess body adipose tissue. Such techniques, however, have a number of drawbacks.
Skinfold calipers use the principle that the amount of subcutaneous adipose tissue correlates to percent body adipose tissue (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). With a skinfold caliper measurement, after the skin is pinched by an operator without inducing pain to the subject, the thickness of the skinfold is measured with the caliper. Caliper measurements of skinfold thickness have been used with various equations developed to predict body density and percent body adipose tissue (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). Most of these equations, however, are sex-specific or only apply to certain populations. Other equations to estimate body density and percent body adipose tissue have been developed using regression models that can take into account data from larger population based studies (Jackson, A. S., Pollock, M. L., Br J Nutr, 1978: 497-504 (1978)).
Even with these improvements, however, skinfold calipers are subject to several serious sources of errors. First, skinfold caliper measurements are heavily operator dependent. The force used to pull back the skin by the operator and the location of the measurement site may vary significantly between different operators, or the same operator, resulting in poor reproducibility of measurements. Second, even though skinfold caliper measurements are based on the assumption that subcutaneous adipose tissue thickness correlates to percent body adipose tissue, skinfold calipers cannot measure the thickness of subcutaneous adipose tissue directly. Skinfold caliper measurements, instead, provide an estimate of subcutaneous adipose tissue thickness which, in turn, is then used to estimate percent body adipose tissue. Thus, two approximations are used to estimate percent body adipose tissue. Third, skinfold caliper measurements may overestimate subcutaneous adipose tissue thickness. When the skinfold is pulled back for the measurement, adipose tissue from adjacent sites can be pulled toward the measurement site causing an artificial increase in the amount of subcutaneous adipose tissue present in the selected body region. This problem is exaggerated in subjects with very elastic soft-tissue. Fourth, the inaccuracies associated with skinfold caliper measurements have lead to the use of equations requiring measurements of 3 body sites, 4 body sites, and even 7 body sites (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). However, even with these adjustments, the inherent inaccuracies of skinfold caliper measurements, most importantly the inability to measure subcutaneous adipose tissue thickness directly, cannot be completely compensated.
Hydrostatic weighing is commonly considered the gold standard for determining body density and estimating percent body adipose tissue. Hydrostatic weighing relies on Archimedes"" principle. A body submerged in water is buoyed by a counterforce equal to the weight of the water that it displaced. Bone and muscle tissue are denser than water, while adipose tissue is less dense. Therefore, a person with low percent body adipose tissue will have higher body density and weighs more in water than a person with higher percent body adipose tissue and the same air weight. Conversely, a person with higher percent body adipose tissue for the same air weight will weigh less in water.
Although hydrostatic weighing is considered the gold standard for body adipose tissue determinations, it is subject to several sources of error. First, hydrostatic weighing requires estimation of pulmonary residual volume, which may vary significantly between individuals. Although pulmonary residual volume can be measured using pulmonary function tests, this adds extra time and expense to the procedure, which could decrease patient compliance. Second, hydrostatic weighing does not account for the variability in bone density known to exist between different individuals and races (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). In patients with high bone density, hydrostatic weighing will underestimate percent body adipose tissue. Conversely, in osteoporotic patients, hydrostatic weighing may seriously overestimate percent body adipose tissue. Third, hydrostatic weighing requires large and expensive displacement chambers, and complete patient immersion in water. The technical requirements and the expense of hydrostatic weighing limit its use in frequent longitudinal measurements of percent body adipose tissue that are desirable in ambulatory patients undergoing a nutritional regimen or exercise induced adipose tissue reduction. Fourth, submersion of the head underwater may be difficult or anxiety provoking for some individuals.
Ultrasonic examination has been used by the inventors of the present invention for assessing subcutaneous fat and muscle layer thickness (see PCT application PCT/US97/18993). While the previous inventions addressed and improved probe interrogation and positioning, reproducibility of ultrasonic measurements of subcutaneous fat and muscle layer thickness could be further improved by reducing other types of operator induced errors in ultrasonic probe positioning.
For example, to measure a fat layer, the probe may be placed in the abdominal region, the supraclavicular region, the suprailiac region, or the thigh region. These regions are, however, often difficult to reproducibly locate and frequently include anatomical areas stretching over several square centimeters of potential interrogation sites, which leads to significant variability in ultrasonic probe placement. This can result in inaccurate repeat measurements if probe placement is not generally maintained over the original interrogation site.
The variability in probe placement and in resultant ultrasonic measurements is typically even greater when measurements are not performed by a trained operator or when self-measurements are obtained. This variability in probe position and alignment decreases the reproducibility of the ultrasonic measurements which is of particular importance when repeat measurements are obtained at different time intervals as a means of detecting a longitudinal change in physiologic parameters measured by ultrasound. Repeat measurements of subcutaneous fat thickness are, for example, critical for monitoring the effects of a diet. Repeat measurements of muscle layer thickness are important for monitoring the effects of a physical exercise program.
Consequently, the present inventors have recognized the need for methods and devices for improving the accuracy and reproducibility of ultrasonic probe positioning and ultrasonic measurements. Methods and devices are provided herein that aid in positioning of ultrasonic probes.
The present invention describes for the first time the use of methods and devices for positioning an ultrasonic probe reproducibly on a subject""s body surface with use of external reference landmarks. Such methods or devices help to improve the reproducibility of ultrasonic measurements, such as measurements of the thickness of a tissue layer such as the subcutaneous fat layer or the muscle tissue layer.
The invention provides for an ultrasonic system for interrogation of an antomical region, such as an abdomen or an appendage. The primary use of such a system is to interrogate an adipose or muscle tissue layer in an abdomen or an appendage. Typically, the ultrasonic system includes an ultrasonic probe for handheld interrogation of a human abdomen, and an an umbilicus positioning unit for positioning the ultrasonic probe in an umbilicus of the human abdomen. Usually, the system includes a computational unit, which can be designed to calculate layer thickness (e.g. an adipose layer) or, if desired, body fat. Preferably, the computational unit can process signals in A scan mode or may be designed to only process signals in A scan mode.
One embodiment of the umbilicus positioning unit typically comprises a bulb to fit in a human umbilicus while permitting the ultrasonic probe to be in acoustic contact with the human abdomen. The bulb can be secured at a predetermined dimension from the ultrasonic probe. Alternatively, the umbilicus positioning unit can comprise a positioning member on a face of the ultrasonic probe to position the ultrasonic probe directly over the umbilicus. Typically, the ultrasonic transducers are oriented to project a beam through the tissue to assess layer thickness or some other property of the tissue. The umbilicus positioning unit can include a pressure sensor to detect, directly or indirectly, pressure on a face of the probe. The umbilicus positioning unit and the computational unit can be encased in a housing. Preferably, such housing is handheld. The umbilicus positioning unit usually reduces variations in ultrasonic measurement of the thickness of human abdomen layer(s) by providing a consistent reference site for interrogation. The umbilicus positioning unit may include a plastic member shaped to snugly fit in an umbilicus. Umbilicus positioning units described herein can be used to make anatomically compatible ultrasonic probes.
The umbilicus positioning unit is typically designed with a positioning member that engages an umbilicus while permitting acoustic contact of the ultrasonic probe with the human abdomen or interrogation sites at other locations. The umbilicus positioning unit, for instance, can include an arm that connects the positioning member to the ultrasonic probe. The arm may be of a predetermined distance, as well as extendable or retractable or both. The arm permits the ultrasonic probe to interrogate the human abdomen or other anatomical regions at a predetermined distance from an umbilicus.
The umbilicus positioning unit is often designed with a tip that engages, or forms a portion of, a housing that holds the ultrasonic probe. The unit may be constructed to permit the ultrasonic probe to generally transmit through the tip. Other embodiments may have substantially no diagnostically relevant transmission through the tip, such as for adjacent interrogation. The tip is typically between about 1 cm and about 4 cm in length. It can have a selected diameter sized to in fit in an umbilicus of choice.
The invention also provides for a handheld, ultrasonic probe. A handheld, ultrasonic probe may include at least a first ultrasonic source to transmit an ultrasonic pulse to a human abdomen, at least a first ultrasonic detector to detect ultrasonic waves from the human abdomen, and an umbilicus positioning unit to position the ultrasonic source and detector. The umbilicus positioning unit and the probe are sized for inclusion in a handheld structure for interrogation of the human abdomen or other site. Often the umbilicus positioning unit will comprise an integral part of the housing of the device. The ultrasonic source and detector can be solely transmitter and receiver transducers, such as for BUA or SOS, or included in the same transducer, such as for A scan. The handheld device may optionally contain a computational unit. Typically, the probe and the computational unit are encased in a housing and the entire unit is handheld. Preferably, the computational unit calculates layer thickness in the object and the probe, and the computational unit and a display are adapted for A-scan.
The invention also provides for an umbilicus positioning unit that can be attached to an ultrasonic probe. Many existing and future probes can benefit from the invention by the attachment of an umbilicus positioning unit. Typically, an attachable umbilicus positioning unit comprises a polymeric material that is shaped or molded to the form of the probe""s exterior. The umbilicus positioning unit can be designed with a friction fit member sized for an ultrasonic probe. The umbilicus positioning unit may slidably and snugly engage the handheld ultrasonic probe. The umbilicus positioning unit may be designed to permit 1) positioning of the ultrasonic probe when interrogating an abdomen and 2) removal of the umbilicus positioning unit from the handheld ultrasonic probe to allow interrogation of other anatomical regions without the umbilicus positioning unit attached to the handheld ultrasonic probe.
The invention also provides for an ultrasonic probe with an anatomical reference member, such as an anatomically compatible ultrasonic probe holder. The anatomical reference member can be used by an operator to permit interrogation in a controllable fashion with respect to a selected anatomical site that may or may not be the site of interrogation. Typically, a first end of the anatomical reference member is positioned with respect to an anatomical site and either a second end or first portion of the anatomical reference member engages or contains an ultrasonic transducer. Usually, the first end engages, holds, or otherwise fits a desired anatomical region. Usually, a handheld, ultrasonic probe includes at least a first ultrasonic source to transmit an ultrasonic pulse to a tissue, at least a first ultrasonic detector to detect ultrasonic waves from the tissue, and an anatomical reference member for reducing probe misplacement and increasing reproducibility of probe positioning with respect to a pre-selected anatomical region for which the anatomical reference member is adapted. The first ultrasonic source and detector, and the anatomical reference member are usually sized for inclusion in a handheld structure for interrogation of the tissue. The probe can include a computational unit. The ultrasonic probe can also include a plurality of separate transducers, such as at least three ultrasonic sources and at least three ultrasonic detectors.
The anatomical reference member can be of a single length or extendable or retractable or both. The anatomical reference member for instance can include an extendable and retractable member to controllably change the distance between the anatomical reference member and the first ultrasonic source and detector or multiple transducers. The anatomical reference member can be designed to allow the first ultrasonic source to transmit generally through the umbilicus positioning unit for diagnostic transmission. Alternatively, the first ultrasonic source may not transmit generally through the anatomical reference member. The anatomical reference member can include a securing member of a substantially flat surface. The securing member stabilizes the probe on the interrogation surface, such as on a surface of an abdomen.
The first ultrasonic source and detector may be disposed in the anatomical reference member. For instance, the anatomical reference member can comprise a ring disposed with respect to the first ultrasonic source and detector at a predetermined distance. The ring is of sufficient diameter to permit a finger to enter the ring and touch a desired anatomical region. The ring permits the operator to controllably position the anatomical reference member and the first ultrasonic source and detector with respect to the desired anatomical region. Alternatively, the anatomical reference member may comprise a convex surface disposed with respect to the first ultrasonic source and detector at a predetermined distance. The convex surface is of sufficient diameter to engage a desired anatomical region. The convex surface permits the operator to controllably position the anatomical reference member and the first ultrasonic source and detector with respect to the desired anatomical region. The convex surface permits interrogation of a site, such as a wrist.
The invention also provides for a kit for monitoring and enhancing adipose tissue loss comprising devices described herein and various health treatments.